Sheet processing apparatus and sheet processing method

ABSTRACT

A sheet direction inverting apparatus has a switchback portion for inverting the conveying direction of mails and the switchback portion has a drive roller and a driven roller. The length of mails sent to nips of the two rollers in the conveying direction is detected by a sensor, and after switching back, the length of the mails sent from the switchback portion in the conveying direction is detected by a sensor, and an overlapped sheets detector compares detection results. When the detection results are different, the overlapped sheets detector detects overlapping of the mails.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of co-pendingapplication U.S. patent application Ser. No. 11/009,385 filed on Dec.13, 2004 (now U.S. Pat. No. 7,201,370) for which priority is claimedunder 35 U.S.C. § 120. This application also claims priority under 35U.S.C. § 119(a) on Japanese Patent Application No. 2003-419-463 filed inJapan on Dec. 17, 2003. The entire contents of each of these applicationare herein fully incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a sheet processing apparatus having adetector for detecting overlapping of taken-out sheets and a sheetprocessing method.

BACKGROUND OF THE INVENTION

For example, as described in U.S. Pat. No. 5,505,440 (Apr. 9, 1996), asan apparatus for processing sheets, a mail processing apparatus fortaking out mails one by one and reading information from them,postmarking the position of each postage stamp, and then stacking themrespectively on stackers corresponding to reading results is known. Thisapparatus has a shingler conveyor for positively shifting mails takenout in an overlapped state and detecting overlapping. The mails detectedoverlapping by the shingler conveyor are rejected without beingprocessed.

The shingler conveyor has a pair of belts for holding mails and movingin the same direction at different speeds and also has an upper streamside sensor for detecting the length of each of mails sent to theshingler conveyor in the conveying direction and a lower stream sidesensor for detecting the length of each of mails sent out from theshingler conveyor in the conveying direction. And, the shingler conveyorcompares the lengths of the mails measured by the two sensors, judgesthat when the lengths are different, overlapped sheets are mutuallyshifted, and detects overlapping.

However, for example, although two mails in the overlapped state areshifted, they cannot be shifted so that the lengths of the mails in theconveying direction are varied and when the shingler conveyor cannotdetect overlapping of the sheets, to the canceling unit arranged on thelower stream side in the conveying direction, the mails are sent in theoverlapping state. In this case, when canceling the stamps with apostmark, a problem arises that the canceling unit cancels the stamp ofthe mail only on the canceling hub with a postmark or the cancelingposition is shifted.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a sheet processingapparatus for precisely detecting overlapped sheets.

According to the present invention there is provided a sheet processingapparatus comprising a switchback portion configured to receive conveyedsheets and send them in an opposite direction, thereby invert aconveying direction of the sheets; a first detector to detect lengths ofthe sheets in the conveying direction before being received by theswitchback portion; a second detector to detect lengths of the sheets inthe conveying direction after being sent from the switchback portion;and a first overlapped sheets detector to detect overlapping of thesheets when detection results of the first and second detectors aredifferent.

Furthermore, according to the present invention there is provided asheet processing method comprising inverting a conveying direction ofsheets conveyed in a first direction so as to convey them in a seconddirection opposite to the first direction; detecting lengths of thesheets to be conveyed in the first direction in the conveying direction;detecting lengths of the sheets to be conveyed in the second directionafter the conveying direction is inverted in the conveying direction;and detecting that the sheets are overlapped when the detected lengthsof the sheets to be conveyed in the first and second directions in theconveying direction are different.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the sheet processing apparatusrelating to the embodiment of the present invention;

FIG. 2 is an operation illustration for explaining the operation ofarranging the front and back and the top and bottom of each mail;

FIG. 3 is a front view showing the structure of a switchback portion tobe incorporated into the sheet processing apparatus shown in FIG. 1;

FIG. 4 is a partially enlarged view showing one switchback structure ofthe switchback portion shown in FIG. 3;

FIG. 5 is a side view of the switchback structure shown in FIG. 4;

FIG. 6 is a perspective view for explaining the structure of the rollerportion of the driven roller of the switchback structure shown in FIG.4;

FIG. 7 is a schematic view for explaining the behavior when a mailenters between the drive roller and the driven roller;

FIG. 8 is a schematic view showing the state that overlapped mails aresent to the switchback portion;

FIG. 9 is a schematic view showing the state that overlapped mails areheld and moved between the nips of the drive roller and driven rollerrotating in the switchback portion;

FIG. 10 is a schematic view showing the state that the rotation of thedrive roller is stopped and the driven roller keeps rotation by theinertia;

FIG. 11 is a schematic view showing the state that the rotation of thedriven roller is stopped and the drive roller starts the reverserotation;

FIG. 12 is a schematic view showing the state that the driven rollermakes the driven rotation in correspondence to the reverse rotation ofthe drive roller;

FIG. 13 is a schematic view showing the state that two mails in theshifted state are separated from the switchback portion; and

FIG. 14 is a flow chart for explaining the operation of processing mailsusing the overlapped sheets detection function of the switchbackportion.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the embodiment of the present invention will be explainedin detail with reference to the accompanying drawings. In FIG. 1, as asheet processing apparatus relating to the embodiment of the presentinvention, a schematic diagram of mail processing apparatus 100(hereinafter, referred to as just processing apparatus 100) is shown.

Processing apparatus 100 has, in the conveying direction of mails M(sheets), feed hopper 101, detector 102 (second overlapped sheetsdetector), OCR scanner 103, twist inverting unit 104, switchback portion105, canceling unit 106, sorted sheets stacker 107, and conveyingportion 108 for conveying mails M through the units. Further, processingapparatus 100 has an operation panel not shown in the drawing forinstructing various operations to the apparatus, switching the operationmode, and displaying errors. Further, when detector 102 detectsoverlapping of mails M, first reject portion 102′ for rejecting mails Mis installed in the neighborhood of detector 102. Furthermore, asdescribed later, when overlapped sheets detector 110 detects overlappingof males M, second reject portion 107′ for rejecting mails M isinstalled as a part of sorted sheets stacker 107.

Feed hopper 101 receives a large amount of standard-size mails M (thelength in the conveying direction may be different) having a thicknesswithin a predetermined range and a fixed width in the directionperpendicular to the conveying direction, takes out them one by one, andfeeds them to the processor on the latter stage. Conveying portion 108conveys fed mails M via processors 102 to 107 on the latter stage.

Detector 102 detects metals, foreign substances, and hard substancesincluded in conveyed mails M by conveying portion 108 and detects doubletaking (that is, overlapping) of mails M and a short gap (the distancebetween the rear end of first mail M conveyed earlier and the front endof succeeding second mail M conveyed following first mail M is shorterthan a predetermined distance). Mails M in which metals, foreignsubstances, or hard substances are detected, mails M in which doubletaking, that is, overlapping is detected, and mails M in which a shortgap is detected are respectively rejected into first reject portion102′. Particularly, detector 102, for example, as indicated in U.S. Pat.No. 5,505,440 (Apr. 9, 1996), has a shingler conveyor for shiftingoverlapped mails M by a pair of belts for holding mails M and moving inthe same direction at different speeds, compares the length of mails Msent to the shingler conveyor in the conveying direction with the lengthof mails M sent out from the shingler conveyor, thereby detectsoverlapped sheets.

OCR scanner 103 optically reads the surface of each mail M,photo-electrically converts it, and obtains sorted sheets informationsuch as the zip code and recipient address recorded on mail M as animage. Further, OCR scanner 103 detects the existence and position of apostage stamp or postal indicia put on mail M. The directions (front,back, top, and bottom) of mails M fed via feed hopper 101 are variable,so that OCR scanner 103 has at least two scanners for reading bothsurfaces of mails M.

Inverting unit 104 has a reversion path (not shown in the drawing) forconveying mails M while twisting in an 180° arc around the central axisof mails M extending in the conveying direction. Namely, inverting unit104 reverses only the front and back without changing the conveyingdirection of mails M. Further, inverting unit 104 has a bypass route(straight path) (not shown in the drawing) for bypassing sent mails Mwithout sending to the reversion path.

Switchback portion 105 has a switchback structure (described later indetail) for receiving conveyed mails M, sending them in the oppositedirection, thereby inverting the conveying direction of mails M.Switchback portion 105, similarly to inverting unit 104 mentioned above,has a bypass route (straight path) (described later) for bypassing theswitchback structure.

Canceling unit 106 has a canceling hub not shown in the drawing whichrotates by rolling and touching one surface of each mail M to beconveyed. In canceling unit 106, the canceling hub rolls and touches theposition of the stamp, thereby cancels the stamp with a postmark. Inthis embodiment, all mails M conveyed to canceling unit 106 passinverting unit 104 and switchback portion 105 and as described later,the front and back and the top and bottom are arranged, so that thecanceling hub is installed only on one side of the conveying route.

Sorted sheets stacker 107, according to the sorted sheets informationdetected by OCR scanner 103, stacks sorted sheets of respective mails Mat a predetermined sorted-sheets position. Further, sorted sheetsstacker 107 has second reject portion 107′ for rejecting mails M whoseoverlapping is detected by switchback portion 105 by prohibitingcanceling by canceling unit 106.

On the other hand, inverting unit 104 and switchback portion 105 have afunction for arranging the front and back and the top and bottom of allmails M fed in the state that the front and back and the top and bottomthereof are set variedly as shown in FIG. 2 and sending them tocanceling unit 106.

For example, mail Ma whose posture is detected by OCR scanner to be theone indicated by A shown in FIG. 2 passes the straight path of invertingunit 104, then passes the straight path of switchback portion 105, andis sent to canceling unit 106 in the unchanged posture. Further, mail Mbwhose posture is detected to be the one indicated by B shown in FIG. 2passes the reverse path of inverting unit 104, then passes theswitchback path of switchback portion 105, is put into the same postureas that of mail Ma, and is sent to canceling unit 106. Further, mail Mcwhose posture is detected to be the one indicated by C shown in FIG. 2passes the sheet twist path of inverting unit 104, then passes thestraight path of switchback portion 105, is put into the same posture asthat of mail Ma, and is sent to canceling unit 106. Furthermore, mail Mdwhose posture is detected to be the one indicated by D shown in FIG. 2passes the straight path of inverting unit 104, then passes theswitchback path of switchback portion 105, is put into the same postureas that of mail Ma, and is sent to canceling unit 106. Namely, all mailsM passing inverting unit 104 and switchback portion 105 are put into thesame posture and are fed to canceling unit 106.

Next, by referring to FIG. 3, the structure of switchback portion 105mentioned above will be explained more in detail. Switchback portion 105has main conveying route 1 for conveying mails M in the direction ofarrow T shown in the drawing. With respect to all mails M sent toswitchback portion 105 via main conveying route 1, the position of eachpostage stamp is detected by OCR scanner 103. Further, with respect tomails M sent to switchback portion 105, the front and back are invertedby inverting unit 104 when necessary.

On one side (on the lower side in FIG. 3) of main conveying route, firstprocessor 2 and second processor 4 are installed side by side. Further,on main conveying route 1, switching gates G1 and G2 for branching andconveying mails M conveyed via main conveying route 1 respectively tofirst processor 2 and second processor 4 are installed.

First processor 2 has first switchback structure 2 a for receiving mailsM branched and conveyed from main conveying route 1 via gate G1 andsending them in the opposite direction, thereby inverting the conveyingdirection of mails M and first U-turn path 2 b for passing mails Mswitched back by first switchback structure 2 a. Namely, mails Mbranched and conveyed to first processor 2 are switched back first andthen are conveyed by a U-turn. And, mails M passing first processor 2and inverted in the conveying direction, via conveying route to an exit6, installed under first and second processors 2 and 4 in the drawing,extending almost in parallel with main conveying route 1, are conveyedin the direction of arrow T′ shown in the drawing and are sent tocanceling unit 106.

Second processor 4 has second U-turn path 4 a for passing mails Mbranched and conveyed from main conveying route 1 via gate G2 and secondswitchback structure 4 b for receiving mails M passing second U-turnpath 4 a, sending them in the opposite direction, thereby inverting theconveying direction thereof. Namely, mails M branched and conveyed tosecond processor 4 are firstly conveyed by a U-turn and then areswitched back. And, mails M passing second processor 4 and inverted inthe conveying direction are led to conveying route to an exit 6 viaunification portion 7 and is sent to canceling unit 106.

Further, main conveying route 1, via unification portion 8 on the lowerstream side of two gates G1 and G2 in the conveying direction, isconnected to conveying route to an exit 6 on the lower stream side ofunification portion 7 in the conveying direction. Main conveying route 1on the upper stream side of unification portion 8 is curved via drumroller 1 a and U-turn path 1 b (bypass route, straight path). And, mailsM passing gates G1 and G2 and passing first and second processors 2 and4 are not inverted in the front and back and the top and bottom and aresent to canceling unit 6 via main conveying route 1 and conveying routeto an exit 6. Further, the length of each conveying route mentionedabove and the processing time of first and second switchback structures2 a and 4 b are designed so that mails M sent to switchback portion 105via main conveying route 1 are all conveyed to unification portion 8 onconveying route to an exit 6 in the same time.

Further, in switchback portion 105, first switchback structure 2 a offirst processor 2 is arranged in a nest shape inside second U-turn path4 a of second processor 4. Further, second switchback structure 4 b ofsecond processor 4 is arranged in a nest shape inside first U-turn path2 b of first processor 2. In other words, fist switchback structure 2 aand second switchback structure 4 b are arranged so as to be overlappedwith each other and first U-turn path 2 b and second U-turn path 4 a arearranged so as to be overlapped with each other.

Namely, by use of a structure that mails M are switched back by oneprocessor, and then the front and back thereof are inverted, and mails Mare inverted in the front and back by the other processor, and then theyare switched back, the size of the apparatus in the arranging directionof first and second processors 2 and 4 can be contracted and theapparatus constitution can be miniaturized. Particularly, when thestructure that inside the U-turn path of one processor, the switchbackstructure of the other processor is arranged in a nest shape is usedsimilarly to switchback portion 105 mentioned above, the apparatus sizecan be effectively miniaturized.

Further, in this embodiment, on the lower stream side of unificationportion 8 in the conveying direction, conveying route to an exit 6 makesa U-turn round drum roller 9 and supply portion 10 a and dischargeportion 10 b of mails M to switchback portion 105 are arranged so as tobe set on the left of switchback portion 105 in the drawing.

Further, switchback portion 105 has a plurality of sensors for detectingpassing of mails M on each conveying route. Namely, sensor S₁ isarranged on main conveying route 1 on the upper stream side of gate G1in the conveying direction, and sensor S₂ is arranged on main conveyingroute 1 between gates G1 and G2, and sensor S₃ (first detector) isarranged on the conveying route branched toward first processor 2 atgate G1, and sensor S₄ (first detector) is arranged on the conveyingroute branched toward second processor 4 at gate G2, and sensor S₅(second detector) is arranged on conveying route to an exit 6, andsensor S₆ is arranged in the neighborhood of discharge portion 10 b ofmails M.

Hereinafter, switchback structure 2 a mentioned above will be explainedmore in detail by referring to FIGS. 4 to 7. FIG. 4 is a plan viewshowing the detailed structure of first switchback structure 2 a.Further, FIG. 5 is a side view of first switchback structure 2 a viewedin the direction (the direction of arrow A in FIG. 4) of sending mailsM. Further, second switchback structure 4 b has a structure that firstswitchback structure 2 a is inverted right and left, so that here, firstswitchback structure 2 a will be explained representatively and theexplanation of second switchback structure 4 b will be omitted.

First switchback structure 2 a (hereinafter, referred to as justswitchback structure 2 a) has drive roller 14 and driven roller 16rotating forward and backward by motor 12 (FIG. 5). Rollers 14 and 16are mutually pressed via conveying route 13. Further, switchbackstructure 2 a, via nips N between two rollers 14 and 16, has guide plate21 extending along the bottom side of conveying route 13.

Drive roller 14 has rotating shaft 14 a extending almost perpendicularlyand two roller portions 14 b and 14 c. Two roller portions 14 b and 14 care fixed to rotating shaft 14 a separated vertically from each otheralong rotating shaft 14 a. The base end of rotating shaft 14 a isattached rotatably and fixedly to main body 11 of switchback portion105. Namely, in main body 11, housing 15 having a plurality ofincorporated bearing not shown in the drawing are fixed and rotatingshaft 14 a is extended through the housing. Further, to the base end ofrotating shaft 14 a extended through housing 15, the rotating shaft ofmotor 12 is directly connected.

On the other hand, driven roller 16 has rotating shaft 16 a fixed tomain body 11. Rotating shaft 16 a does not rotate for main body 11. Onrotating shaft 16 a, two roller portions 16 b and 16 c (described later)formed by an elastically deformable material are installed separatelyfrom each other in the axial direction and are independently attachedrotatably to rotating shaft 16 a. Namely, two roller portions 16 b and16 c are attached respectively to rotating shaft 16 a via two bearings17. Further, two roller portions 16 b and 16 c are respectivelypositioned so as to roll and touch two roller portions 14 b and 14 c ofopposing drive roller 14.

The inter-shaft distance between drive roller 14 and driven roller 16 isset so that roller portions 14 b, 16 b, 14 c, and 16 c are pressed viaconveying route 13. Namely, rotating shafts 14 a and 16 a of two rollers14 and 16 are respectively attached to main body 11 with a fixedposition relationship, so that roller portions 16 b and 16 c of drivenroller 16 are elastically deformed as shown in the drawing, thuspressure is generated between the two. Further, roller portions 16 b and16 c of driven roller 16 are elastically deformed, thus mails M arepermitted to pass.

Further, switchback structure 2 a has take-in conveying route 22 forsending mails M toward nips N in the direction of arrow A shown in thedrawing and take-out conveying route 23 for sending mails M in theopposite direction from nips N, that is, in the direction of arrow Bshown in the drawing. Namely, switchback structure 2 a has conveyingstructure 25 for conveying mails M in the direction of arrow A viatake-in conveying route 22 and conveying mails M in the direction ofarrow B via take-out conveying route 23. Conveying structure 25 has aplurality of conveying rollers 26 and a plurality of endless conveyingbelts 27 wound and stretched round conveying rollers 26.

Further, on take-in conveying route 22, sensor S₃ mentioned above fordetecting passing of mails M is installed. Sensor S₃ is installed, onthe basis of the time from passing of the front end of each mail M inthe conveying direction to passing of the rear end thereof in theconveying direction, to detect the length of each mail M in theconveying direction. Sensor S₃ is installed to obtain deceleration,stop, and acceleration timing of drive roller 14 and is installed todetect overlapping of mails M. Further, sensor S₅ mentioned abovefunctions similarly to sensor S₃ and is installed to detect the lengthsof mails M in the conveying direction. Further, before and after nips N,sensors 32 and 33 are installed. Two sensors 32 and 33 are installed todetect the existence of mails M at nips N.

Switchback structure 2 a having the aforementioned structure operates asindicated below. When mails M are sent in the direction of arrow A viatake-in conveying route 22 by conveying structure 25, passing of mails Mis detected by sensor S₃, and the lengths thereof in the conveyingdirection are detected, and the front ends of concerned mails M in theconveying direction rush into nips N between drive roller 14 and drivenroller 16. At this time, drive roller 14 is rotating clockwise anddriven roller 16 is follow-rotating in the same direction as that ofdrive roller 14. When mails M pass nips N, roller portions 16 b and 16 cof driven roller 16 are elastically deformed and follow mails M.

And, after mails M rush into nips N, drive roller 14 is decelerated atpredetermined timing and mails M are stopped. This state is shown inFIG. 4. At this time, driven roller 16 intends to continue the rotationby the inertia force.

After mails M are stopped, lever 28 is rotated in the posture shown inFIG. 4 by a drive structure not shown in the drawing and taps on theleft end of stopped mails M in the drawing. Lever 28, hereafter, isreturned to its home position (not shown in the drawing) by sensor 29.By doing this, the concerned end is directed downward to makepreparations for the reverse operation.

Hereafter, drive roller 14 is accelerated and rotated in the oppositedirection and mail M held and stopped by nips N is accelerated in thedirection of arrow B, is transferred to conveying structure 25, and istaken out via take-out conveying route 23. By doing this, the conveyingdirection of mail M is inverted. Further, when mails M are acceleratedin the opposite direction by drive roller 14, driven roller 16 intendsto continue to stop by the inertia force.

Hereinafter, by referring to FIG. 6, roller portion 16 b of drivenroller 16 will be explained more in detail. Further, roller portion 16 chas the exactly same structure as that of roller portion 16 b, so thatroller portion 16 b will be explained here representatively.

Roller portion 16 b has an elastically deformable two-layer structurethat the outside first layer in contact with roller portion 14 b ofdrive roller 14 is formed by rubber 41 (a solid elastic body) and theinside second layer is formed by sponge 42 (a foamed elastic body). Inthis embodiment, outside rotation shaft 16 a, via a bearing not shown inthe drawing, aluminum core metal 43 is installed, and sponge 42 isinstalled outside core metal 43, and rubber 41 is installed outsidesponge 42. Further, thickness t1 of rubber 41 is set to 2 [mm], andthickness t2 of sponge 42 is set to 13 [mm], and the diameter of coremetal 43 is set to 20 [mm], and the diameter of roller portion 16 b isset to 50 [mm]. Further, the width of roller portion 16 b is set to 15[mm]. Further, roller portions 14 b and 14 c of drive roller 14 are alsoformed by the same rubber material as rubber 41 of roller portions 16 band 16 c of driven roller 16.

As described above, driven roller 16 is arranged fixedly in the statethat it is pressed to drive roller 14, so that when mail M is rushedinto nips N, driven roller 16 will not spring up from conveying route13. Namely, in this case, driven roller 16 is deformed according to thethickness of mails M as shown in FIG. 5 and holds and conveys mails Mpassing nips N while always giving pressure to them. Therefore, theconveying force by drive roller 14 is effectively transferred to mails Mand mails M are prevented from changing in the conveying speed.

Next, by referring to FIG. 7, the behavior of driven roller 16 (rollerportion 16 b) and mails M when mails M rush into nip N will beconsidered. Further, driven roller 16, in the state before mails M reachnip N, rolls and touches drive roller 14 so as to transfer the driveforce and follow-rotates in the direction of the arrow shown in thedrawing.

When mails M rush into nip N, roller portion 16 b is crushed and mails Mare slowly held between it and roller portion 14 b of drive roller 14.At this time, roller portion 16 b gives force R perpendicular to theroller surface to mails M. Therefore, on mails M, reaction force RCosθpressing back mails M in the opposite direction of the converyingdirection (the direction of arrow T shown in the drawing) is acted.Reaction force RCosθ increases as mails M become thicker.

On the other hand, mails M are conveyed in the direction of arrow T byconveying force F based on the rotation of roller portion 14 b andconveying force F′ base don the rotation (follow rotation) of rollerportion 16 b. Therefore, if the resultant force of conveying forces Fand F′ acting on mails M is sufficiently larger than reaction forceRCosθ, mails M are normally conveyed, while when conveying forces F andF′ are reduced, defective conveyance is caused.

Names, when the dynamic friction coefficients of roller portions 14 band 16 b to mails M are low, conveying forces F and F′ are reduced andthe aforementioned effect of reaction force RCosθ is increased.Therefore, to normally convey mails M, it is necessary to increaseconveying forces F and F′, that is, the dynamic friction coefficients ofroller portions 14 b and 16 b to mails M as large as possible.

Further, to obtain normal conveying performance, other than increasingthe dynamic friction coefficient, a method for reducing the elasticityof roller portion 16 b so as to decrease reaction force RCosθ may beconsidered. Therefore, in this embodiment, roller portion 16 b has atwo-layer structure internally having sponge 42. Further, the hardnessand thickness of sponge 42 are necessary conditions for obtaining thefollow deformation performance to mails M and a appropriate pressure bymutual action. When the hardness is too high or the thickness is toosmall, follow deformation is difficult, and defective conveyance iscaused, and mails M and rive roller 14 (peripheral members included) aredamaged. Namely, to normally invert mails M by switchback portion 105mentioned above, it is necessary to set the dynamic frictioncoefficient, hardness, and thickness of roller portion 16 b toappropriate values.

Next, the operation when inverting mails M non-uniform in thickness byswitchback portion 105 having the aforementioned structure, particularlytaking notice of the behavior of two rollers 14 and 16, will beexplained. Further, here, as shown in FIG. 5, a case of conveying mailsM non-uniform in thickness such that the thickness of the side (theupper side in the drawing) held and conveyed by two roller portions 14 band 16 b installed above in the axial direction is thicker than thethickness of the side (the lower side in the drawing) held and conveyedby two roller portions 14 c and 16 c installed below will be explained.

As described above, roller portions 16 b and 16 c of driven roller 16are formed by an elastically deformable material and according to thethickness of mails M passing nips N between roller portions 14 b and 14c of drive roller 14, the deformation amount thereof is changed. In thisembodiment, roller portion 16 b for holding and conveying the thick sideof mails M has a larger deformation mount than that of roller portion 16c for holding and conveying the thin side. In other words, in this case,the apparent radius of roller portion 16 b is smaller than the apparentradius of roller portion 16 c.

Therefore, as mentioned above, when mails M non-uniform in thickness aresent via conveying route 13 and pass nips N, the angular speed of rollerportion 16 b having a smaller radius is higher than the angular speed ofroller portion 16 c having a larger radius. Namely, the moving speeds ofthe outer peripheral surfaces of roller portions 16 b and 16 c rotatingin contact with mails M are the same, so that the angular speed ofroller portion 16 b having a smaller radius is higher. Although theangular speeds are different, the moving speeds of the outer peripheralsof roller portions 16 b and 16 c, that is, the peripheral speeds are thesame.

Inversely, when roller portions 16 b and 16 c are fixed to rotationshaft 16 a, the angular speeds of roller portions 16 b and 16 c arephysically the same, so that a difference is generated in the peripheralspeed between two roller portions 16 b and 16 c having differentradiuses. When a difference is generated in the peripheral speed betweentwo roller portions 16 b and 16 c like this, a difference is generatedin the conveying speed of mails M, and mails M are not only crinkled andskewed but also in the worst case, are broken.

Therefore, in this embodiment, roller portions 16 b and 16 c arerotatably attached independently of rotation shaft 16 a. By doing this,the angular speeds of roller portions 16 b and 16 c can be madedifferent from each other and the roller portions can respond to mails Mnon-uniform in thickness.

Namely, according to this embodiment, two roller portions 16 b and 16 cinstalled on the same axle of driven roller 16 can rotate independentlyof rotation shaft 16 a, so that even when holding and conveying mails Mnon-uniform in thickness, mails M can be surely conveyed free ofwrinkles, skews, and failures such as ruptures.

Next, the shingler operation for overlapped mails M by switchbackportion 105 will be explained by referring to FIGS. 8 to 11. Further, inFIGS. 8 to 11, for simplicity of drawing, sensors S₃ and S₅ areinstalled at the same position.

The shingler operation of mails M by switchback portion 105 is performedsimultaneously while switchback portion 10 is performing the reverseoperation. Here, the shingler operation of mails M by first switchbackstructure 2 a will be explained representatively. However, the shingleroperation can be performed similarly by second switchback structure 4 b.

As shown in FIG. 8, when two mails M1 and M2 overlapped in the statethat the respective front ends are shifted at a distance of l₁ passsensor S₃ and are sent to first switchback structure 2 a, as shown inFIG. 9, two mails M1 and M2 are overlapped just in the state that therespective front ends are shifted at a distance of l₁ and rush into nipsN between drive roller 14 and driven roller 16. When mails M1 and M2rush into nips N, driven roller 16 follows drive roller 14 and rotatesat the same peripheral speed as that of drive roller 14.

Hereafter, when drive roller starts deceleration at predetermined timingto invert mails M1 and M2, mail M1 in contact with drive roller 14 alsostarts deceleration at the same time. On the other hand, mail M2 incontact with driven roller 16 is controlled by driven roller 16intending to continue the even speed rotation by the inertia force andintends to continue the movement at the uniform rate. In this case, thefriction coefficient between rollers 14 and 16 and mails M1 and M2 islarger than the friction coefficient between mails M1 and M2, so thatfor mail M1 decelerated, mail M2 intending to keep the uniform rate isshifted.

Furthermore, even when drive roller 14 is stopped, mail M2 intends tocontinue the movement by the inertia force of driven roller 16, so thattwo mails M1 and M2 are shifted more and as a result, as shown in FIG.10, the distance at which the respective front ends of mails M1 and M2are shifted becomes l₂. Distance 12 is shorter than distance l₁. And, asshown in FIG. 11, when stopped drive roller 14 starts reverse rotation,this time, driven roller 16 intends to continue the stop by the inertiaforce thereof, so that mail M2 controlled by driven roller 16 intends tocontinue the stop. At this time, two mails M1 and M2 are shifted more.As a result, the distance at which the respective front ends (the rearends in the moving direction) of mails M1 and M2 are shifted becomes l₃.

Furthermore, as shown in FIG. 12, when the rear end of mail M on theside of drive roller 14 in the moving direction passes nips N, mail M2controlled by driven roller 16 until now makes contact with drive roller14. Hereafter, shifted mail M2 is held and restricted by drive roller 14and driven roller 16, is given conveying force, and is sent in theopposite direction and as shown in FIG. 13, the distance at which therespective rear ends of mails M1 and M2 are shifted becomes l₄ and themails are moved. Distance 14 is longer than distance 13.

Mails M1 and M2 sent to switchback structure 2 a in the overlapped stateas mentioned above are shifted automatically and surely during thenormal reverse operation. When two mails M1 and M2 are shifted byswitchback structure 2 a like this, the lengths of mails M1 and M2 inthe overlapped state in the conveying direction are changed. In thisembodiment, the lengths of mails M1 and M2 are detected by sensor S₃ (insecond switchback structure 4 b, sensor S₄) and S₅ installed before andafter switchback structure 2 a, and length changes are detected byoverlapped sheets detector 110 (first overlapped sheets detector), thusoverlapping of mails M is detected. And, for mails M1 and M2 whoseoverlapping is detected by overlapped sheets detector 110, canceling bycanceling unit 106 is inhibited and they are rejected to second rejectportion 107′ installed in sorted sheets stacker 107.

On the other hand, detector 102 mentioned above also detects overlappingof mails M and rejects them to first reject portion 102′. However, forexample, when two mails M1 and M2 mentioned above are shifted by theshingler conveyor and then as shown in FIG. 8, are sent in the statethat mail M2 is completely overlapped on mail M1, detector 102 does notdetect length changes between mails M1 and M2 in the conveyingdirection, so that overlapping cannot be detected. Namely, depending onthe shift direction and shift amount by the shingler conveyor ofdetector 102, a case of the state shown in FIG. 8 may be considered.When mails M1 and M2 whose overlapping is not detected by detector 102like this are sent to canceling unit 106 as they are, a problem arisesthat only the mail on the canceling hub side is canceled or the normalposition is not canceled.

On the other hand, as indicated in this embodiment, switchback portion105 detects overlapping of mails M, so that even mails M whoseoverlapping cannot be detected by detector 102 can be surely shifted anddetected. Particularly, by matching the shift direction of mails M bydetector 102 with the shift direction of mails M by switchback structure2 a (4 b), shifted mails M are prevented from returning to detector 102and mails M can be shifted more surely.

Hereinafter, by referring to the flow chart shown in FIG. 14, theoperation of processing overlapped mails M using the overlapped sheetdetection function of switchback portion 105 will be explained.

When mail M is taken out by feed hopper 101 (Step S1), on the basis ofdetection results by OCR scanner 103, the feed hopper judges whether ornot concerned mail M must be switch backed concerned mail M (Step S2).

As a result of judgment at Step S2, when it is judged that concernedmail M must be switched back (Step S2, YES), concerned mail M passes theswitchback path of switchback portion 105 and the conveying directionthereof is inverted (Step S4).

At this time, by sensor S₃ (or S₄), passing of the front and rear endsof concerned mail M to be sent to the switchback path in the conveyingdirection is detected (Step S3) and from the conveying speed and passingtime, the length of concerned mail M in the conveying direction isdetected by overlapped sheets detector 110. Further, at this time, bysensor S₅, passing of the front and rear ends of concerned mail Mpassing the switchback path and sent from switchback portion 105 isdetected (Step S5) and the length of concerned mail M in the conveyingdirection is detected by overlapped sheets detector 110.

And, overlapped sheets detector 110 compares the length detected at StepS3 with the length detected at Step S5 and when it judges that thedetected lengths are equal (Step S6, YES), overlapped sheets detector110 judges that one mail M is conveyed normally (not overlap). In thiscase, concerned mail M is sent to canceling unit 106 as it is, iscanceled the stamp with a postmark (Step S7), and is stacked in apredetermined sorted sheets stacker according to detection results byOCR scanner 103 (Step S8).

On the other hand, as a result of judgment at Step S2, when it is judgedthat there is no need to switch back concerned mail M (Step S2, NO),concerned mail M passes the straight path of switchback portion 105 andis sent to canceling unit 106 and the canceling process at Step S7 andthe sorted sheets stacking process at Step S8 are performed.

Further, as a result of judgment at Step S6, when overlapped sheetsdetector 110 judges that the lengths of concerned mail M in theconveying direction before and after switchback are different (Step S6,NO), overlapped sheets detector 110 judges that concerned mail M isoverlapped, inhibits canceling when mail M passes canceling unit 106(Step S9), and then rejects concerned mail M to second reject portion107′ of sorted sheets stacker 107 (Step S10).

Hereafter, it is judged whether there is rejected mail M in secondreject portion 107′ or not (Step S11), and when it is judged that thereis rejected mail (Step S11, YES), the operation is stopped atpredetermined timing, and mail M is taken out from second reject portion107′ by an operator, and it is fed again by hand (Step S12). On theother hand, as a result of judgment at Step S11, when it is judged thatthere is not mail M in the rejected sheets stacker (Step S11, NO), theoperation is finished.

Further, the present invention is not limited straight to theaforementioned embodiment and at the execution stage, within a rangewhich is not deviated from the object of the present invention, thecomponents may be modified and actualized. Further, by appropriatecombination of a plurality of components disclosed in the aforementionedembodiment, various inventions can be formed. For example, from all thecomponents indicated in the aforementioned embodiment, some componentsmay be deleted.

For example, in the aforementioned embodiment, as a switchback portion,the structure that the driven roller is pressed to the drive roller isexplained as an example. However, the present invention is not limitedto it and a switchback portion having a pair of belts that one beltfollows the other belt may be used.

Further, the shift direction of overlapped mails M is not limited to theone of the aforementioned embodiment.

Furthermore, sheets are not limited to mails and as other sheets,banknotes and securities may be used.

The sheet processing apparatus of the present invention has theaforementioned constitution and operation, so that overlapped sheets canbe shifted by the switchback portion, and overlapping of sheets can bedetected easily and surely, and the canceling unit can be prevented fromdefective canceling. Further, by the sheet processing method of thepresent invention, overlapping of sheets can be detected easily andsurely and defective canceling can be prevented surely.

1. A sheet processing apparatus comprising: a switchback portionconfigured to receive conveyed sheets and send them in an oppositedirection, thereby invert a conveying direction of the sheets; a firstdetector to detect lengths of the sheets in the conveying directionbefore being received by the switchback portion; a second detector todetect lengths of the sheets in the conveying direction after being sentfrom the switchback portion; and a first overlapped sheets detector todetect overlapping of the sheets when detection results of the first andsecond detectors are different, wherein the switchback portion includesa drive roller, driven to rotate in both forward and backwarddirections, on one side of the sheets, and a driven roller, followingthe sheets, in a state that the sheets are held between the drive rollerand the driven roller, and wherein the switchback portion is soconstructed that: two overlapping sheets are shifted with respect toeach other when the rotation of the driving roller is decelerated in theforward direction because a sheet contacting the drive roller slows downaccording to the deceleration of the drive roller, while the other sheetcontacting the driven roller is maintained at a constant speed byinertial rotation of the driven roller; and the two overlapping sheetsare more shifted with respect to each other when the driving roller isrotated in the backward direction because the sheet contacting the driveroller moves in the backward direction according to the backwardrotation of the drive roller, while the other sheet contacting thedriven roller is stopped because the driven roller is maintained at restby inertia.
 2. (canceled)
 3. The sheet processing apparatus according toclaim 1 further comprising: a feed hopper configured to feed the sheets;a conveying portion configured to convey the fed sheets; a cancelingunit configured to cancel the sheets sent from the switchback portion;and a first reject portion configured to prohibit canceling the sheetswhose overlapping is detected by the first overlapped sheets detector bythe canceling unit and reject them.
 4. The sheet processing apparatusaccording to claim 3 further comprising: a second overlapped sheetsdetector to detect overlapping of the fed sheets; and a second rejectportion configured to reject the sheets whose overlapping is detected bythe second overlapped sheets detector.
 5. (canceled)
 6. A sheetprocessing method comprising: inverting a conveying direction of sheetsconveyed in a first direction so as to convey them in a second directionopposite to the first direction; detecting lengths of the sheets to beconveyed in the first direction in the conveying direction; detectinglengths of the sheets to be conveyed in the second direction after theconveying direction is inverted in the conveying direction; anddetecting that the sheets are overlapped when the detected lengths ofthe sheets to be conveyed in the first and second directions in theconveying direction are different, wherein the inverting of theconveying direction of the sheets is executed by a switchback portionand the switchback portion includes a drive roller, driven to rotate inboth forward and backward directions, on one side of the sheets, and adriven roller, following the sheets, in a state that the sheets are heldbetween the drive roller and the driven roller; and shifting twooverlapping sheets with respect to each other by decelerating a sheetcontacting the drive roller according to the drive roller indeceleration, while maintaining the speed of the other sheet contactinga driven roller by inertial rotation of the driven roller; and shiftingthe two overlapping sheets to a further degree with respect to eachother by driving the sheet contacting the drive roller according todrive roller in backward direction while maintaining the other sheetcontacting the driven roller at rest by inertia.
 7. (canceled)
 8. Thesheet processing method according to claim 6 further comprising: feedingthe sheets; conveying the fed sheets in the first direction; cancelingthe sheets inverted and conveyed in the second direction; andprohibiting canceling the sheets whose overlapping is detected andrejecting them.
 9. The sheet processing method according to claim 8further comprising: detecting overlapping of the sheets fed and conveyedin the first direction; and rejecting the sheets conveyed in the firstdirection when detecting that the sheets conveyed in the first directionare overlapped.
 10. (canceled)